During red tide events aerosolized polyether brevetoxins (PbTxs) have been linked to upper and[unreadable] lower airway symptoms in both normal individuals and in "susceptible populations", i.e. those individuals with[unreadable] pre-existing airway disease. During the first grant cycle we showed that sheep inhaling PbTxs environmentally[unreadable] relevant concentrations of PbTx developed adverse pulmonary events including acute bronchoconstriction,[unreadable] airway hyperresponsiveness (AHR), airway inflammation and decreased mucociliary clearance. Both normal[unreadable] and allergic sheep, which serve as a surrogate for a "susceptible population", responded to toxin challenge, but[unreadable] the severity of the response was, in part, dependent on the underlying inflammatory status of the airways. The[unreadable] most striking findings, however, were that the airway effects of the inhaled PbTxs differed in their physiological[unreadable] actions and their response to pharmacologic intervention. The differences in responses were related to[unreadable] changes in the chemical structure of the PbTx tested. To further complicate the problem, we found that a[unreadable] natural congener of PbTx and chemically modified PbTxs not only could block the adverse pulmonary effects[unreadable] of PbTx, but in some instances, improve pulmonary function on their own. These findings suggest that[unreadable] synthetic and/or natural modifications of the PbTx molecules can result in the generation of compounds that[unreadable] have increased toxicity, or depending on the structural modification, beneficial effects in the airway. Therefore,[unreadable] in this proposal we will test the hypothesis that the severity of the airway effects of inhaled toxins, i.e.[unreadable] effects on bronchial tone, airway responsiveness, mucociliary clearance, inflammatory cell recruitment[unreadable] and airway cell function are dependent on the chemical structure(s) of the individual PbTxs that are[unreadable] aerosolized. Furthermore, we postulate that the PbTx congeners and analogs can stimulate different[unreadable] pulmonary cells/receptors and that the PbTx-induced effects (whether beneficial or harmful) will be dependent[unreadable] on cells/receptors on various pulmonary cells stimulated by the toxins. Three Specific Aims will be used to[unreadable] test this hypothesis. Specific Aim 1: A) To compare the effects of selected PbTxs (both natural and synthetic[unreadable] toxins), PbTx congeners and toxin complexes identified in field studies on measures of bronchial tone[unreadable] (pulmonary airflow resistance, RL) and mucociliary clearance (tracheal mucus velocity, TMV and whole lung[unreadable] mucociliary clearance, MCC) to identify the chemical structure(s) responsible for the observed effects whether[unreadable] beneficial or harmful. And B) To use in vivo pharmacology to identify airway cells/receptors responsible for[unreadable] toxin-induced effects. Specific Aim 2: To determine the mechanisms responsible for the airway inflammation[unreadable] and airway hyperresponsiveness (AHR) that result from 4-day PbTx exposure, including the regulation of[unreadable] nuclear factor kappa beta (NFkB) activation, subsequent cytokine release and the role of adhesion molecule[unreadable] activation. Specific Aim 3: To determine if the immunosuppressive effects of PbTx on macrophages and the[unreadable] PbTx-induced depressions in TMV seen after toxin exposures affect bacterial clearance in vivo. We will[unreadable] continue to utilize the sheep model for these studies because this model responds to inhaled concentrations of[unreadable] toxin that are present in the environment and cause respiratory symptoms in humans and comparisons[unreadable] between normal and allergic sheep allow us to model airway effects in "normal" and "susceptible populations".[unreadable] Furthermore, as demonstrated in the Progress Report / Preliminary Studies, the physiologic endpoints[unreadable] measured in this model have adequate sensitivity to differentiate amongst the PbTx congeners that differ by a[unreadable] single atom or functional group, thereby providing confidence that the proposed Specific Aims can be[unreadable] accomplished. The data generated in this proposal are novel in that they provide an approach to understanding[unreadable] how structure and composition of aerosolized toxin affects the airways. The experiments are being conducted[unreadable] at environmentally relevant concentrations. Because of our extensive experience with delineating inflammatory[unreadable] cascades in this model, we are well positioned to understand mechanisms involved in toxin-induced[unreadable] inflammation in the airways and the potential of toxin exposure to impair host defense mechanisms. With the[unreadable] current paucity of data addressing these issues, the proposed studies should provide needed information on[unreadable] the pathophysiological consequences of PbTx exposure.